1. The Star Formation- Density Relation …and the Cluster Abell 901/2 in COMBO-17 Christian Wolf (Oxford) Eric Bell, Anna Gallazzi, Klaus Meisenheimer (MPIA Heidelberg) Alfonso Aragon-Salamanca, Meghan E. Gray, Kyle Lane (Nottingham)

2. Morphology-Density Relation Morph-density relation –Present when averaged over age/colour (Dressler 1980) –No such relation at fixed colour or age (Ball, Loveday & Brunner 2006; Wolf et al. 2007) at fixed mass (Kauffmann et al. 2004) SFR-/Age-density relation –Yes: at fixed mass (Balogh et al. 1999; Kauffmann et al. 2004; Poggianti et al. 2006) –Yes: at fixed morphology (Wolf et al. 2007)

3. Morphology-Age-Density Wolf et al. 2007 Age-density relation for ageing (E-Sb) galaxies Age-morphology relation for fixed density (obvious?!) No Morphology-density relation at fixed age

4. SF-Density (  ) Relation Gomez et al. 2002 (SDSS) Kodama et al. 2001 Lewis et al. 2002 (2dF) …or nurture? –Stripping (Ram press., Gun & Gott 72) –Excitation (Tidal of burst, Bekki 99) –Harassment (Moore et al. 1999) –Mergers (Major, Barnes 1992) –Suffocation (Larson 1980) –Strangulation (Balogh et al. 2000) Nature? –Internal feedback (SN, AGN)

5. SF-Density Relation Across Z Present-day SF-density –Optical SF indicators GOODS (Elbaz et al. 2007) –z~1, includes obscured SF –SF peaks at higher density Semi-analytic simulations –Typically include mergers, but no environment physics –Recent work: IGM heating + ram-pressure stripping (Khochfar & Ostriker 2007)

6. Low-Z incl. Obscured SF Obscured SF: different result from UV-optical indicators –COMBO-17 A901 + MIPS –Obscured SF continues into high-density regions –Not very different to z~1 Which galaxies make the difference? –See dusty red galaxies (Wolf, Gray & Meisenheimer 2005) (M B <-20) A901 Gallazzi et al., in prep.

7. λ / nm QE (%) COMBO-17 on A901 Complex Disturbed evolving cluster Abell 901a/b & 902 –Galaxy transformation during plenty of infall action –800 cluster members with M V < -17.8 and  z ~ 0.006 5 Mpc

8. Old Red / Dusty Red @ z=0.17 Age  Dust  Old red Dusty red ~150 at M V <-18 Wolf, Gray & Meisenheimer 2005

9. Mean Spectra

10. Type-Density Relation Dusty red galaxies: Intermediate ages Intermediate density Intermediate luminosity Intermediate morphology Non-virialized kinematics  infall population? WGM 2005

11. Optically Passive Spirals! old dusty blue ES0SaSbScSdIrr The STAGES collaboration Passive spirals (Poggianti et al. 1999; Goto et al. 2003) –Spectra & colours: Lack of star formation –Cluster infall regions –Might be intermediate stage from spiral to S0 A901 dusty red galaxies (Wolf, Gray & Meisenheimer 2005) –35%(!) of red members Red star-forming galaxies (Miller & Owen 2002, Coia et al. 2005) –Radio; ISO 15  –Outskirts of merging cluster

12. SFR: UV-opt. vs. Obscured

13. Dust Extinction & IR/UV Ratio

14. Dusty Red = “Transition” Population Dusty red galaxies in A901 are semi-suppressed in star formation have star formation obscured to highest degree star formation obscuration ~ stellar light obscuration All galaxies appear to follow a 2 Gyr exponential SFR decline

15. IR-Semi-Passive Galaxies Transition galaxies –IR-semi-passive spirals ≈1/2-dex-reduced central dust-extinguished SF –No burst upon infall –No sign of major mergers –No truncation (H  weak) Where found? –In three complex merging cluster environments (so far) Star formation budget –Fraction of obscured SF increases in infall region –Small on cosmic scale –Relevant for role of environment –Continued central SF may continue bulge growth

16. Suggestions: Observations Quenching Timescale? –High-S/N spectra + SED –Recent SF History More (super-) clusters? –Density is not only factor –2nd parameter: “Stage” of infall, cluster merging? –Optical SED sufficient(?) –Need: Redshift coverage Range of environments Accurate dust estimates or Mid-IR imaging Medium-band photo-z’s or spectroscopy

17. 80 orbit mosaic ACS + WFPC2/NIC3 parallels multiwavelength follow-up from X-ray to radio primary science aim: galaxy evolution as a function of environment image: COMBO-17 contours: mass Space Telescope A901/902 Galaxy Evolution Survey

19. Ratio Spectrum: Dusty/Old WGM 2005

20. Selecting The Cluster Sample z phot = 0.170 ± 0.006 795 galaxies within  cz = 1900 km/s1575 = 3.7 x 3.5 x 120 (Mpc/h) 3

21. Luminosity Distribution

22. 2-D Clustering Old red = cluster cores Dusty red ~ blue cloud

23. (x,y):old red = cluster cores dusty red ~ blue cloud (y,z):old red ~ dusty red blue cloud = ‘voids’  v ~ 550 km/s  v ~ 1400 km/s